Cold pour acrylic, also called cold cure acrylic is used to make temporary dentures, duplicate dentures, inexpensive basic or affordable dentures and denture repairs. The cold cure acrylic resin is generally processed in an electrically heated pressure vessel. When fabricating a dental prosthesis with cold cure acrylic the waxed prosthetic teeth and cast are placed in a duplicating flask designed for a duplicating material made of either a two part free flowing silicone or melted reversible hydrocolloid to be poured into the duplicating flask creating a negative impression of the waxed prosthesis. When the duplicating material becomes rigid the cast and waxed teeth are separated from the duplicating material where in the wax is removed from the cast and cleaned from the teeth. Once teeth and cast are thoroughly cleaned they are reinserted into the impression material and cold cure acrylic poured in through access holes of the flask. The flask is then placed into the electrically heated pressure vessel and cured at an appropriate pressure and temperature according to manufacturers recommendations. The duplicating materials associated with the cold pour technique however have constraints.
Reversible hydrocolloids require time constraints to chop and melt the material and bring the material to an ideal operating temperature. The ideal operating temperature being a temperature which allows the material to easily flow into a duplicating flask and reflect the detail of the waxed prosthesis without melting the wax and damaging the precise dimensions of the waxed prosthesis. There are also cost constraints with the availability of expensive equipment such as hydrocolloid conditioners designed to melt the hydrocolloid and keep the material at a constant operating temperature all the while mixing the material to keep it from congealing. Also necessary are cold running water baths, which cool the material for removing the waxed prosthesis from the duplicating material in a timely manner. Hydrocolloid is also highly susceptible to distortion when removing the waxed cast from the flexible material and it has poor dimensional stability causing a possible changed in the vertical dimension, affecting the accuracy of the final prosthesis' occlusion.
Free flowing Addition silicones mimic the accuracy of reversible hydrocolloid with a high dimensional stability. No reaction by products are formed as long as the correct proportions of one to one A-silicone are used. To achieve accuracy it is recommended to have a homogeneous mixing of the material to avoid streaks and voids. There are manufacturer-mixing machines available but add to the expense already associated with the higher price material costs of free flowing A-silicone and its single use nature. Free flowing Addition silicones are also limited to a fairly low Shore hardness, usually in the low twenties and teens. Lab silicones with a lower Shore hardness will demonstrate lower stiffness; unfortunately decreased stiffness may allow the matrix to be easily deformed effecting vertical dimension.